Preparation

• Preheat the oven to 350°F (175°C) and prepare a baking sheet by lining it with parchment paper or a silicone mat.
• Mix melted butter, granulated sugar, egg yolk, vanilla extract, and red gel food coloring in a bowl until smooth and creamy.
• Gradually incorporate all-purpose flour, unsweetened cocoa powder, baking soda, and fine salt into the wet ingredients; mix until just combined.
• Divide the dough into six equal portions, roll each into a ball, and lightly coat in granulated sugar before placing on the baking sheet.
• Bake for 10-12 minutes until cookies spread slightly and develop a crackly top. Allow to rest for 2 minutes on the tray before transferring to a wire rack.
• Press a white chocolate heart gently into the center of each cookie while they are still warm, then refrigerate for 30 minutes.